• Analytical Science and Technology
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• v.32 no.5
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• pp.173-184
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• 2019

As the size of semiconductors becomes smaller, it is necessary to perform high precision polishing of nanoscale. Ceria, which is generally used as an abrasive, is widely used because of its uniform quality, but its stability is not high because it has a high molecular weight and causes agglomeration and rapid precipitation. Such agglomeration and precipitation causes scratches in the polishing process. Therefore, it is important to accurately analyze the size distribution of ceria particles. In this study, a study was conducted to select dispersants useful for preventing coagulation and sedimentation of ceria. First, a dispersant was synthesized and a ceria slurry was prepared. The defoamer selection experiment was performed in order to remove the air bubbles which may occur in the production of ceria slurry. Dynamic light scattering (DLS) and asymmetrical flow field-flow fractionation (AsFlFFF) were used to determine the size distribution of ceria particles in the slurry. AsFlFFF is a technique for separating nanoparticles based on sequential elution of samples as in chromatography, and is a useful technique for determining the particle size distribution of nanoparticle samples. AsFlFFF was able to confirm the presence of a little quantities of large particles in the vicinity of 300 nm, which DLS can not detect, besides the main distribution in the range of 60-80 nm. AsFlFFF showed better accuracy and precision than DLS for particle size analysis of a little quantities of large particles such as ceria slurry treated in this study.

• Korean Chemical Engineering Research
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• v.60 no.4
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• pp.613-619
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• 2022

The extended Maxwell-Wagner polarization model is employed to describe the ER(Electrorheological) behavior of bi-dispersed ER suspensions, and solutions to the equation of motion are obtained by dynamic simulation. Under the same particle volume fraction, it is found that the dynamic yield stresses of uniform size suspensions do not depend on the particle size. Compared with uniform size suspensions, the dynamic yield stress is reduced for ER fluids consisting of two kinds of particles with different sizes. Compared with the dynamic yield stress behavior, for ${\dot{\gamma}}^*$≧0.01 the shear stress shows different behaviors depending on the particle sizes and the raio of different size particles. The simulation results show the nonlinear ER behavior (∆_𝛕 ∝ Eⁿ, n ≈ 1.55) of the conducting particle ER suspensions.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.1-4
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• 1999

The attenuation coefficients of SiC particle reinforced low-density polyethylene (LDPE) matrix composites were measured by pulse echo method and dynamic elastic measure method with varying the volume fraction of SiC particle ranged from 0% to 40% and the size of SiC particles ranged from 0.8$\mu$m to 48$\mu$m. The SiCp/LDPE composites were fabricated with the melt injection process and the fabricated composites showed almost full density above 99% up to 40vo1% SiCp reinforcements. The attenuation constant of LDPE measured by dynamic elastic constant had same result with that measured by pulse echo method, but the attenuation constant of SiCp/LDPE measured by dynamic elastic constant did not have same result with that measured by pulse echo method.

• 한국가시화정보학회:학술대회논문집
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• 2004.12a
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• pp.41-45
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• 2004

The dynamic particle image velocimetry (PIV) is consisted of a high frequency pulse laser, high speed cameras and a timing controller. The three velocity components of flow downstream of an axial flow fan for PC cooling system are measured using the dynamic PIV system. An Axial flow fan has seven blades of 72 mm in diameter. The rotating speed is 1800 rpm. The downstream flow is visualized by smoke particles of about $0.3-1\;{\mu}m$ in diameter. The three-dimensional instantaneous velocity fields are measured at three downstream planes. The swirl velocity component was diffused downstream and the change in time-mean vorticity distribution downstream was also discussed. The spatio-temporal change in axial velocity component with the blades passing is recognized by the instantaneous vector maps. And the dynamic behavior of vorticity moving with the rotating blades is discussed using the unsteady vorticity maps.

• Bulletin of the Korean Space Science Society
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• 2004.04a
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• pp.39-39
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• 2004

It has been known that ring current particles can be lost through dayside MP(magnetopause). However, details of the loss mechanism of this process has not received much attention. In this study, we show that the solar wind dynamic pressure P$\sub$D/ can play a significant role in the dayside loss. In order to show that, we have first conducted superposed epoch analysis using 95 geomagnetic storm events selected from the period 1997 to 2002. (omitted)

• Journal of Industrial Technology
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• v.17
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• pp.233-239
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• 1997

The effects of preheating the gas stream on deposition characteristics of ultrafine $SiO_2$ particles were investigated theoretically. The model equations such as mass and energy balance equations and aerosol dynamic equations were solved to predict the particle growth and deposition. The gas temperatures, $SiCl_4$ concentrations, $SiO_2$ particle volumes, $SiO_2$ particle sizes and deposition efficiencies of $SiO_2$ particles were calculated for various preheating temperatures. As the preheater setting temperature increases, the $SiO_2$ particle size distribution becomes more uniform, because the effect of $SiCl_4$ diffusion decreases.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.45.2-45.2
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• 2015

It is obvious that there are plentiful of dust particles in the interplanetary spaces of the Solar System (IDPs), based on micrometeor craters, zodiacal light and direct measurements on the spacecraft. Because of photon drag and planetary perturbations, these particles are continuously falling to the Sun or planets, therefore continuous source of the IDPs are required. We studied the fractional contribution of each type of solar system objects to the IDPs complex through the optical properties of the potential dust sources and the zodiacal light. We found that more than 90% of the IDPs are originated from cometary nuclei. This result is discussed through the comparison with the dynamic simulation, micrometeors mineralogy and near-infrared spectrum of the zodiacal light. In addition, we introduce our new project on the numerical simulation for the dust particles ejected from the cometary nuclei, to verify the conclusion of dominant cometary contribution and its detailed consequences.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.197-203
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• 1998

The discrete element method is a numerical model capable of describing the mechanical behaviour of assemblies of discs and spheres. The method is based on the use of an explicit numerical scheme in which the interaction of the particles is monitored contact by contact and the motion of the particles modelled particle by particle. In this paper, A two-dimensional model for computing contacts and motions of granular particles of unform, inelasticity is presented. And, code is developed. The primary aim of this paper is to approv computational result of continuum alaysis which is on processing. The end of this paper, that code is tested with several examples.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.9-17
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• 2001

A numerical study has been carried out on the evolution of the particle size distribution for unipolar charged particles that experience coagulation in an alternating electric field. The collision frequency function of charged particles was analytically derived. The log-normal size distribution function is utilized for representing a poly-disperse size distribution and the moments of the particle size distribution are used to solve the general dynamic equation considering only AC electric force effect. The results are compared with the effects of brownian coagulation.

• Journal of Industrial Technology
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• v.16
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• pp.157-168
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• 1996

The deposition characteristics of ultrafine $SiO_2$ particles were investigated in a tube furnace reactor theoretically and experimentally controlling tube wall temperature in deposition zone. The model equations such as mass and energy balance equations and aerosol dynamic equations inside reactor and deposition tube were solved to predict the particle growth and deposition. The particle size and deposition efficiencies of $SiO_2$ particles were calculated, changing the process conditions such as tube furnace setting temperature, total gas flow rate inlet $SiCl_4$ concentration and were compared with the experimental results.